1. Field of the Invention
This invention relates generally to the fabrication of a giant magnetoresistive (GMR) read head, more specifically to the fabrication of an abutted junction GMR read head having a free layer of maximal effective length resulting from the elimination of overspreading of the biasing and lead layers.
2. Description of the Related Art
Magnetic read heads whose sensors make use of the giant magnetoresistive effect (GMR) in the spin-valve configuration (SVMR) base their operation on the fact that magnetic fields produced by data stored in the medium being read cause the direction of the magnetization of one layer in the sensor (the free magnetic layer) to move relative to a fixed magnetization direction of another layer of the sensor (the fixed or pinned magnetic layer). Because the resistance of the sensor element is proportional to the cosine of the (varying) angle between these two magnetizations, a constant current (the sensing current) passing through the sensor produces a varying voltage across the sensor which is interpreted by associated electronic circuitry. The accuracy, linearity and stability required of a GMR sensor places stringent requirements on the magnetization of its fixed and free magnetic layers. The fixed layer, for example, has its magnetization “pinned” in a direction normal to the air bearing surface of the sensor (the transverse direction) by an adjacent magnetic layer called the pinning layer. The free layer is magnetized in a direction along the width of the sensor and parallel to the air bearing surface (the longitudinal direction). Layers of hard magnetic material (permanent magnetic layers) or laminates of antiferromagnetic and soft magnetic materials are typically formed on each side of the sensor and oriented so that their magnetic field extends in the same direction as that of the free layer. These layers, called longitudinal biasing (or bias) layers, maintain the free layer as a single magnetic domain and also assist in linearizing the sensor response by keeping the free layer magnetization direction normal to that of the fixed layer when quiescent. Maintaining the free layer in a single domain state significantly reduces noise (Barkhausen noise) in the signal produced by thermodynamic variations in domain configurations. A magnetically stable spin-valve sensor using either hard magnetic biasing layers or ferromagnetic biasing layers is disclosed by Zhu et al. (U.S. Pat. No. 6,324,037).
A common configuration of the longitudinal biasing layer when it is formed of hard magnetic material is the abutted junction, wherein the biasing layer abuts the lateral edges of the GMR sensor element, which have been shaped to produce a smooth, linear contour against which to form the biasing layer. The biasing layer, when so placed, biases the free layer of the sensor element by direct magnetostatic coupling, stabilizing its domain structure and bias point (the orientation of its magnetic moment when quiescent). Zhu et al. (cited above) teaches the formation of an abutted junction having a spacer layer between the hard magnetic biasing layer and the junction region. Lin et al. (U.S. Pat. No. 6,185,078) teaches the formation of an abutted junction wherein a ferromagnetic film magnetostatically couples to a ferromagnetic free layer. Kautzky et al. (U.S. Pat. No. 6,344,953) teaches a configuration in which the biasing layer abuts the sensor in an abutting junction, but the current carrying leads overlay the biasing layer and the top surface of the sensor. Gill (U.S. Pat. No. 5,828,531) also teaches the formation of a spin valve sensor having an abutted junction biasing layer, but with a conducting lead layer that produces a current at an angle to the air bearing surface of the sensor.
The abutted junction has both advantages and disadvantages. An advantage is that it enables a simple and direct definition of the read width of the sensor by physical removal of all portions of the sensor element except that which lies between the hard biasing layers. The necessity of reading magnetic storage media of increasingly higher area densities places stringent requirements on the dimensions of the sensor read width, so the narrow abutted junction formation is advantageous. A disadvantage is that reducing the read width of an abutted junction sensor requires removal of a large portion of the actual element and, therefore, a corresponding reduction of the width of the free layer and loss of signal strength. Another source of reduced signal strength in the abutted junction is a result of the conducting lead layer configuration, which is typically over the biasing layer. Unavoidably, the biasing layer and the conducting lead layer spread over the lateral edge of the sensor, as is illustrated schematically in FIG. 1 (prior art). FIG. 1 shows a schematic cross-sectional view of an abutted junction sensor having a bottom spin valve configuration in which the free layer (8) is positioned at the top of the sensor element (4). The hard biasing layer (2) abuts the sensor element (4), contacting the lateral ends of the free layer and the conducting lead layer (6) is formed over the biasing layer. The dashed circled region shows the overspreading of the biasing layer and the lead layer. This overspread has the disadvantageous effect of reducing the sensitivity of the sensor even beyond the reduction resulting from the narrowed free layer. The overspread allows sensing current carried by the lead layers to be shunted through lateral edge portions of the free layer, reducing its effective usable length and, therefore, its sensitivity.
Although the physical reduction of free layer width is unavoidable in the abutted junction, the overspreading of the conducting lead layer and the biasing layer can be significantly reduced. It is the object of the present invention to provide a method of producing that reduction.